There is sometimes an occasion that a screw equipped with a metal washer and a rubber washer is used for fixing a circuit board (refer to Japanese Patent No. 5853997 as Patent Document 1, for example).
A hole in the metal washer is inserted through a shaft portion so as to be adjacent to a head portion of a screw body, and the rubber washer is inserted through the shaft portion as well.
A hole in the washer-equipped screw disclosed in Patent Document 1 pressed down a circuit board by an elastic force of the rubber washer.
A thermal deformation of the circuit board can also be absorbed by the elastic force of the rubber washer.
In the washer-equipped screw disclosed in Patent Document 1, a projection that contacts with the shaft portion of the screw body is formed on an inner peripheral surface of a hole of the rubber washer, so that the metal washer and the rubber washer do not detach.
The metal washer is provided for receiving a reaction force of a head portion side of the rubber washer in a large area when tightening the screw body.
In the washer-equipped screw with which the metal washer contacts a seat surface of the head portion, the metal washer and the seat surface slide against each other when tightening the washer-equipped screw, and a surface layer of the metal washer or the seat surface may be damaged.
Particularly, when the screw body is fastened to the object to be fixed, the metal washer may slide roughly against the seat surface by the reaction force of the rubber washer.
When plating is applied to at least one of the metal washer and the seat surface, there is a possibility that the plating peels off due to sliding and becomes debris.
In a case of the washer-equipped screw for fixing the circuit board, damaged plating (debris) may cause a short circuit on the circuit board.